I upgraded my m0 freeze to m1, and it' 10 out of 10. I did this with my isida from m0 to m1, and i got to buy isida for "free" (because i had already) So i have freeze m0 with 10/10 upgrade, Why can't i get m1?

And if i can't get m1 ( for some reason) can my m0 freeze be downgraded to m0 0/10 upgrade and the chrystals be returned to my account>?

If your freeze is m0 and you have fully upgrated it to m1 (10/10), you'll get the m1 modification of the turret for free BUT if you have the m2 modification unlocked, you'll have to purchase the m2 at it's price. I don't think you'll be able to get the crystals you spent upgrating back.